Puzzlepedia™ Grid Puzzles
Slitherlink
Connect the dots to form a single loop.
This puzzle (also known as Fences, Takegaki, Loop the Loop, Loopy, Ouroboros, Suriza and Dotty Dilemma) is a popular logic puzzle played on a grid of dots. The objective is to connect adjacent dots with straight lines to form a single loop with no loose ends and without crossing over itself. In addition, the numbers inside some of the cells represent how many of its four sides are part in the loop.
Placing an x on an edge where you know a line cannot be placed can help keep track of the logic.
Another technique is to shade the inside of the loop differently from the outside of the loop. If a shaded square has an x on one of the edges, you can continue the shading across the x. If two adjacent squares are shaded differently, then there must be a line between them. Also, if one side of a line is shaded, then the other side of the line must have the opposite shading.
Corner Patterns
Inferences can be made for any number appearing in a corner. For 1s, you can place an x into each corner edge. For 2s you can place a line on the edges leading into the corner square. For 3s you can place lines on both corner edges. For 0s you can place an x in all for spots in addition to the two edges leading into the corner square.
Patterns for 1s
If a line comes into the corner of a square with a 1, and it cannot turn away from the square, then you can place an x on the opposite edges.
If two 1s are diagonal and two of the inner connecting edges have an x, then the other two inner edges must also have an x.
Patterns for 2s
If a square with a 2 in it has an x on one of the edges and a line coming into one of the opposite corners, then you know that the line must not turn away from the square and there must be a line adjacent to the x and opposite the incoming line.
Patterns for 3s
Two adjacent 3s must have a line between them and a line on either side.
Two diagonal 3s must have lines on the four outer edges.
A 3 adjacent or diagonal to a 0 forces lines to be drawn according to the diagram.
If a line comes into a square with a 3 in it, you can draw a line on both opposite edges.
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